This disclosure relates generally to the field of providing highly accurate over current fault protection in charging systems in which power converters are used to charge electronic devices and, more particularly, to systems in which the charge over current protection (COCP) and discharge over current protection (DOCP) circuitry in electronic devices are particularly resilient to variations in temperature, printed circuit board (PCB) resistance, and integrated circuit trip voltages.
Power converter circuitry can be used to convert alternating current (AC) power into direct current (DC) power. AC power is typically supplied from wall outlets, and is sometimes referred to as line power. Electronic devices include circuitry that runs from DC power. The DC power that is created by an AC-to-DC power converter may be used to power an electronic device. The DC power that is created may also be used to charge a battery in an electronic device.
In some applications, AC-to-DC power converter circuitry may be incorporated into an electronic device. For example, desktop computers often include AC to DC power converter circuitry in the form of computer power supply units. A computer power supply unit may have a socket that receives an AC power cord. With this type of arrangement, the AC power cord may be plugged directly into the computer to supply AC power without using an external power converter.
Although desktop computers are often large enough to accommodate internal power supplies, other devices such as handheld electronic devices and portable computers may not be. As a result, typical handheld electronic devices and laptop computers require the use of external power converters. When disconnected from the power converter, a handheld electronic device or portable computer may be powered by an internal battery or batteries, such as a Li-ion (i.e., Lithium-ion) battery pack. When an AC line power is available, the power converter is used to convert AC power into DC power for the electronic device.
Compact AC-DC power converter designs are typically based on switched-mode power supply architectures. Switched-mode power converters contain switches, such as transistor-based switches (e.g., field-effect transistor, or “FETs”), that work in conjunction with energy storage components, such as inductive and capacitive elements, to regulate the production of DC power from an AC source. One or more protector integrated circuits (ICs) may be employed in the electronic device being charged that provide a feedback path that may be used to disable the charging process if unsafe charging conditions are sensed in the device being charged.
High power converter efficiency is desirable for conserving power. High power conversion efficiency can be obtained by using efficient converter topologies and low-loss parts. Even when an optimal design is used, however, certain fault conditions may arise in the electronic device that is being charged, e.g., over voltage (OV) conditions, under voltage (UV) conditions, charge over current (COC), discharge over current (DOC), and short circuit (SC) conditions. Variation in the detection of these thresholds may be caused by, e.g.: 1.) temperature/gate drive/process shift-dependent variation in the resistance of FETs being used to sense the charging current in the device being charged; 2.) variation in resistance of the PCB in the device being charged (which can affect the sensed charging current); and 3.) variation in the trip voltage of the one or more protector ICs used in the device being charged.
It would therefore be desirable to provide highly accurate current fault protection circuitry for portable electronic devices having battery packs that is able eliminate or reduce the errors associated with the various causes of fault conditions enumerated above.